The present invention relates to a high-purity copper-chromium alloy that is useful for forming semiconductor copper alloy wiring. In particular, the invention relates to a high-purity copper-chromium alloy sputtering target that allows formation of thin films having excellent uniformity.
Conventionally, Al alloys (specific resistance: about 3.0 μΩ·cm) were used as wiring materials of semiconductor devices. However, copper wiring having a lower resistance (specific resistance: about 2.0 μΩ·cm) has been put into practical use with miniaturization in wiring. Copper wiring is generally formed by forming a diffusion barrier layer of, for example, Ta or TaN in wiring or a wiring groove and then forming a film of copper by sputtering. Copper having a high purity of 5N to 6N is usually produced from electrolytic copper having a purity of about 4N (excluding gas components) as a crude metal by a wet or dry purification process, and the purified copper is used as a sputtering target.
As described above, copper is very effective for semiconductor wiring. However, copper itself is a very active metal and easily diffuses, and therefore causes a problem of contaminating a Si substrate or its periphery through the semiconductor Si substrate or the insulating film thereon. In particular, with progress in miniaturization of wiring, the problem cannot be sufficiently prevented by the conventional diffusion barrier layer of Ta or TaN only, and copper wiring materials themselves are also required to be improved. Accordingly, as copper wiring materials, copper alloys prepared by adding manganese (Mn) or chromium (Cr) to copper (Cu) and having a so-called self-diffusion suppression function (electromigration resistance) by self-forming a barrier layer through a reaction of Mn or Cr in the Cu alloys with oxygen in an insulating film have been proposed.
The semiconductor copper alloy wiring is formed using a copper-chromium alloy or copper-manganese alloy sputtering target. In such semiconductor copper alloy wiring, the in-plane variation in film thickness or sheet resistance of the wiring layer, which has not conventionally caused any problem, causes a problem of reducing the yield of chips (product) prepared from a wafer with progresses of miniaturization, density growth, and integration of semiconductor devices and with progresses of miniaturization and increase in number of wiring layers. Accordingly, there is a demand for a copper alloy sputtering target that can form a thick film (wiring) with less variation.
The present invention is focused on, in particular, a high-purity copper-chromium alloy sputtering target. Known related technologies are shown below.
Patent Document 1 describes a method of producing a low-oxygen high-density Cu/Cr sputtering target through: a stage of forming a powder mixture having a total oxygen content less than 900 ppm by mixing a Cu powder having a grain size controlled within a range of about 20 to 150 μm and a Cr powder having a grain size controlled within a range of about 20 to 150 μm; and a stage of compressing this powder mixture for at least about 1 hour such that the density is at least 90% of the theoretical density. Patent Document 1, however, does not have any description about the problems of Cr dispersibility and impurities.
Patent Document 2 describes a Cu-based sputtering target for forming electrode films, a method of producing the target, and a Cu-based electrode film. In the sputtering target, a phase of a transition metal element (e.g., Cr, Co, Mo, W, Fe, Nb, or V) that is not solid-soluted into a matrix mainly made of Cu is dispersed in the matrix. As an example, a Cu-10 at % Cr target is shown. Patent Document 2, however, does not have any description about the problems of Cr dispersibility and impurities.
Patent Document 3 describes a method of producing a high-density sputtering target composed of a Cr—Cu alloy that is a compressed target material such that a bulk density is 30% to 50% of the theoretical value and that a ratio of the radius to the thickness is 5 or more. Patent Document 3, however, does not have any description about the problems of Cr dispersibility and impurities.
Patent Document 4 describes a material for conductive wire produced from a copper alloy containing: Cu in an amount exceeding 90 at %; at least one element selected from the group consisting of Ca, Sr, Ba, Sc, Y, lanthanide, Cr, Ti, Zr, Hf, and Si in a total amount of 0.5 to 10 at %; and at least one element selected from the group consisting of Mg, V, Nb, Ta, Mo, W, Ag, Au, Fe, and B in a total amount of 0 to 5 at %. Patent Document 4, however, does not have any description about the problems of Cr dispersibility and impurities.
Patent Document 5 describes a copper sputtering target and a method of producing it. The copper sputtering target is composed of Cu and at least one alloy element selected from the group consisting of Al, Ag, Co, Cr, Ir, Fe, Mo, Ti, Pd, Ru, Ta, Sc, Hf, Zr, V, Nb, Y, and rare earth metals in a total amount of 0.001 to 10 wt %, and has a very small grain size and high electromigration resistance. Patent Document 5, however, does not have any description about the problem of Cr dispersibility.
Patent Document 6 describes a sputtering target for forming semiconductor copper alloy wiring, which is a semiconductor element wiring material proposed by the present applicant and is composed of Mn in an amount of 0.05 to 5 wt %, at least one element selected from Sb, Zr, Ti, Cr, Ag, Au, Cd, In, and As in a total amount of 10 wt ppm or less, and the remainder being Cu.
This is effective for enhancing the self-diffusion suppression function, but the purpose thereof is not a reduction in in-plane variation of the copper alloy thin film formed on a wafer.
Patent Document 7 describes a copper alloy sputtering target, a method of producing it, and semiconductor device wiring. The copper alloy sputtering target contains Al in an amount of 0.01 to less than 0.5 wt %, Mn in an amount of 0.25 wt ppm or less, and at least one element selected from Sb, Zr, Ti, Cr, Ag, Au, Cd, In, and As in a total amount of 1.0 wt ppm or less. Patent Document 7, however, does not have any description about the problem of Cr dispersibility.
Patent Document 8 describes a copper alloy sputtering target and semiconductor device wiring. The copper alloy sputtering target contains Al in an amount of 0.5 to 4.0 wt %, Si in an amount of 0.5 wt % or less or Sn in an amount of 0.5 to 4.0 wt %, Mn in an amount of 0.5 wt ppm or less, and at least one element selected from Sb, Zr, Ti, Cr, Ag, Au, Cd, In, and As in a total amount of 1.0 wt ppm or less. Patent Document 8, however, does not have any description about the problem of Cr dispersibility.
Patent Document 8 discloses a technology relating to semiconductor device wiring using a copper-chromium alloy, but there is no recognition about problems of chromium contained in the alloy. This point is common to all Patent Documents mentioned above.
Patent Document 1: JP 2001-073127 A
Patent Document 2: JP H11-50242 A
Patent Document 3: JP 4435386 B
Patent Document 4: JP 2008-506040 A
Patent Document 5: JP 2010-502841 A
Patent Document 6: JP 2006-73863 A
Patent Document 7: International Publication No. WO2004/083482
Patent Document 8: JP 2009-114539 A